1. Field of the Invention
The present invention relates in general to electrolytic cells and, more particularly, to an electrolytic cell and the associated process for the formation of an electrolytic cell, wherein a primer comprised of lithium silicate and carbon is placed between the current collector and the electrode active material to substantially reduce contact resistance and consequently increase columbic efficiency while providing excellent electrochemical/chemical stability.
2. The Prior Art
Rechargeable, or secondary cells, have been known in the art for many years. Furthermore, secondary cells constructed with a primer placed between the current collector and the active material have likewise been known in the art. (See for example, U.S. Pat. No. 5,262,254 to Koksbang, et al.) Although such lithium rechargeable batteries have proven to be functional, they have not solved the problem of relatively high interfacial resistance between the electrode active material and the current collector. Indeed, it is well known that the power density and cycle life of such rechargeable batteries is reduced due to this increased level of cell resistance.
The electrode current collector of an electrolytic cell serves the primary function of conducting the flow of electrons between the active material of the electrode and the battery terminals. Fluctuations in the surface contacts between the active material and the current collector, therefore, increase the internal resistance of an electrolytic cell thereby decreasing both cycle life and power density. Therefore, what is needed, is an interface or "primer" layer between the current collector and the electrode active material which will promote and maintain contact between the electrode active material and the current collector so as to minimize the internal resistance of the cell.
In order to decrease the interfacial resistance between the current collector and the electrode active material, various approaches have been pursued, including chemical and mechanical modifications of the current collector surface layer. Although such modifications have proven helpful, they exhibited high levels of interfacial resistance due to inadequate mechanical and electrical contact between the current collector and the electrode active material as well as the inability to increase electronic conductivity. Furthermore, because of their chemical composition, these modifications have been limited to use on only one of the two electrodes, usually the anode.
Although the prior art does disclose the use of a primer, none of said art discloses the use of an alkali metal silicate and carbon based primer to reduce contact resistance and to enhance the columbic efficiency of the cell while providing excellent chemical/electrochemical stability. U.S. Pat. No. 5,262,254 ("'254 patent") to Koksbang, et al. discloses the use of a carbon based primer on the positive electrode current collector which prevents corrosion to the positive electrode current collector from the electrolyte. Furthermore, the '254 patent requires that the carbon based primer contain one or more conductive polymers and is only applied to the positive electrode current collector. Accordingly, while the use of the carbon/polymer primer in Koksbang, et al. serves to prevent corrosion of the positive electrode current collector--it does not utilize a primer comprised of carbon and a metal polysilicate, nor is the primer in Koksbang et al. capable of serving as a means of reducing contact resistance and consequently increasing columbic efficiency in either or both of the positive or negative electrodes.
European Patent Application 93, 111,938.2 discloses the use of a lithium silicate in conjunction with both carbon and a binder for use solely as the anode active material. The lithium silicate serves to absorb and release lithium ions during cell operation by electrochemical reactions in a nonaqueous electrolyte.
It is thus an object of the present invention to provide an electrolytic cell having a primer composed of an alkali metal polysilicate and carbon, without a binder, which is operatively placed between the electrode active material and its current collector.
It is also an object of the present invention to provide an electrolytic cell having a primer which is chemically and electrochemically stable so as to reduce contact resistance and consequently enhance the columbic efficiency of an electrolytic cell.
It is still further an object of the present invention to provide an electrolytic cell wherein a primer compound of an alkali metal polysilicate and carbon is applied to one or both of an anode and cathode current collector.
These and other objects of the present invention will become apparent in light of the attached Specification, Claims, and Drawings.